Dialects can be defined as "sub-forms of languages which are, in general, mutually comprehensible".[1] English speakers from different countries and regions use a variety of different accents (systems of pronunciation), as well as various localized words and grammatical constructions; many different dialects can be identified based on these factors. Dialects can be classified at broader or narrower levels: within a broad national or regional dialect, various more localized sub-dialects can be identified, and so on. The combination of differences in pronunciation and use of local words may make some English dialects almost unintelligible to speakers from other regions.

The major native dialects of English are often divided by linguists into three general categories: the British Isles dialects, those of North America, and those of Australasia.[2] Dialects can be associated not only with place, but also with particular social groups. Within a given English-speaking country, there will often be a form of the language considered to be Standard English – the Standard Englishes of different countries differ, and each can itself be considered a dialect. Standard English is often associated with the more educated layers of society.

The following are portmanteaus devised to describe certain local varieties of English and other linguistic phenomena involving English. Although similarly named, they are actually quite different in nature, with some being genuine mixed languages, some being instances of heavy code-switching between English and another language, some being genuine local dialects of English used by first-language English speakers, and some being non-native pronunciations of English. A few portmanteaus (such as Greeklish and Fingilish) are transliteration methods rather than any kind of spoken variant of English.

^Fischer 2004, p. 181 "[T]he goal [of constructed languages] is no longer of practical use... Living languages are of far greater influence in the world ... world languages are emerging naturally for the first time in history. Indeed, the English language -- by historical circumstance, not by design -- presently counts more second-language speakers than any other tongue on Earth and numbers are growing."